When I bought the car the glass was visibly wobbling on the test drive. One of very few faults, but anyway...
The seller 'sorted it' before I picked it up, but inaccurately - one corner/edge of the glass was fouling the main cowling of the mirror body and causing it to jam when tilting.
I got it home, pulled the glass off, and did it properly. From memory, the glass came away from whatever bit clips into the motor. Stuck a few of those sticky pads on the back of the glass, lined it up and stuck it on.